Following the progress of immunology and blood transfusion in recent years, component transfusion in which only blood components required for treating various diseases are transfused has become more popular than conventional whole blood transfusion. Blood component transfusion is an outstanding transfusion treatment exhibiting a high curative effect, while mitigating the load on patients during transfusion. Various blood preparations used for the blood component transfusion, such as concentrated erythrocytes, concentrated platelets, and platelet poor plasma, are prepared by centrifuging whole blood obtained by donation. However, it has become known that side reactions are induced after transfusion due to the leukocytes contained in these blood preparations because the blood preparations obtained by centrifugation contain many leukocytes. The side reactions after transfusion include comparatively slight side reactions, such as headache, nausea, a chill, and a non-hemolytic exothermic reaction, as well as serious side reactions such as induction of graft versus host (GVH) reaction to a patient with an immune disorder in which the transfused leukocytes has a death-inducing effect on the skin and internal organs of the recipient, infection by viruses present in leukocytes such as cytomegalovirus infection, and alloantigen sensibilization. Removing leukocytes from the blood preparations is effective in preventing such side reactions after transfusion.
There has been an increasing demand for the technology of removing leukocytes from patient's peripheral blood for medical treatment of systemic erythematodes, chronic or malignant rheumatoid arthritis, Behcet's disease, idiopathic thrombo-cytopenic purpura, autoimmune hepatitis, chronic ulcerative colitis, Crohn's disease, atopic dermatitis, rapidly progressive glomerulonephritis, and systemic inflammatory response syndrome, and for the purpose of immune suppression before transplant. Leukocyte removal is practiced also in the field of heart surgery, wherein leukocytes are removed from the blood perfused after coronary-artery bypass surgery to mitigate a hindrance effect by activated leukocytes.
Methods for removing leukocytes from blood are broadly classified into a centrifuge separation method, making use of differences in the specific gravity of blood components, and a filter method using a fibrous medium such as non-woven fabric or a porous sponge-like material having three-dimensional continuous pore networks as a filter. The filter method is more popular due to higher leukocyte removal efficiency, simple procedure, and lower cost.
Polymer materials consisting these leukocyte-removal filters are generally hydrophobic and cause other useful blood components such as platelets to adhere when removing leukocytes. It has been difficult to achieve a balance between the leukocyte-removal efficiency and the platelet recovery efficiency. Development of a material that can selectively remove leukocytes, while allowing platelets to pass through, has been strongly desired, particularly for patients with a disease, in which a decrease in platelets is undesirable, such as idiopathic thrombocytopenic purpura or autoimmune hepatitis.
When an aqueous-type liquid containing platelets such as blood is caused to come in contact with a material, the higher the hydrophilicity of the surface of the material, the more difficult it is for the platelets to become activated and the easier it is for a water layer to be formed on the material surface by the hydrogen bond of water and the material, whereby adsorption of platelets and hydrophobic proteins can be inhibited. Therefore, various hydrophilic polymers have been developed to modify the surface of materials and methods for introducing such polymers onto the surface of materials by graft polymerization or coating are known in the art. JP-A 2000-245833 discloses a filter material for selectively removing leukocytes. The material allows erythrocytes and platelets to pass through, but does not allow leukocytes to pass through. In the filter material, the above problems have been overcome by coating a hydrophilic polymer onto the material forming the filter. One possible problem with the coated filter material is elution of the hydrophilic polymer from the surface. Although the possibility of the polymer elution into an aqueous solution is very low, a material with a smaller risk of elution has been desired for use in processing of a large amount of blood, such as that used for extracorporeal circulation, to ensure stability of the filter material when it is kept in contact with an aqueous solution such as blood for a long time.
JP-A 07-25776 discloses a filter material coated with a polymer having both hydrophobic groups and hydrophilic polyethylene oxide chains. This is a filter material with a reduced risk of polymer elution by decreasing the solubility of the polymer in an aqueous solution by introducing hydrophobic groups into the polymer. However, since the polymer has both hydrophobic groups and hydrophilic groups having opposite properties each other in the polymer molecule, the action of hydrophobic portions through which the polymer is caused to adhere to the filter supporting body which consists the filter material is reduced. It has, therefore, been difficult to ensure a balance between filter performance and elution properties using this technology alone. The inventors of the present invention examined this technology using a polymer made from methyl methacrylate and methoxypoly(ethylene glycol methacrylate) having polyethylene oxide chains. As a result, the present inventors have found that aqueous solutions become turbid due to polymer elution.
The present inventors have further found that a specific removing material surface can absorb viruses, remove leukocytes, and recover platelets and filed a patent application on the invention covering this finding (PCT/JP 02/10766, WO 03/033035). Although this prior patent application describes the same polymer as the polymer of the present invention as an example of the polymer for forming a specific surface, the prior invention differs from the present invention in that the claimed filter removes viruses simultaneously with leukocytes. In addition, the inventors of the present invention coated a specific supporting body with the polymer described in the prior application as one embodiment, of which the conditions of polymerization and purification differ from those applied to the present invention, and evaluated elution of the polymer. As a result, the present inventors have found that a slight degree of elution occurred, although the degree was not so remarkable as to cause the test solution to become turbid. It is needless to mention that it is more desirable to further suppress the elution taking into consideration the application of the filter in a medical treatment.
There have been no high performance polymers used for filters for selective removal of leukocytes exhibiting both high safety and high blood filtration performance at the same time.